The present invention relates to the de-icing of air inlet cowls of jet engines, particularly aircraft engines.
It is known that, if need be (to prevent the formation of ice or to remove ice which has already formed), the leading edge of the air inlet cowl of such engines is de-iced by heating it with pressurized hot air tapped from said engine and conveyed to said leading edge by a pressurized hot air circulation circuit.
To this end, such an air inlet cowl comprises, in the known way:
a hollow leading edge delimiting an internal annular peripheral chamber, closed by an internal partition (or bulkhead) and provided with at least one orifice placing said annular chamber in communication with the outside; and
a hot air supply pipe capable of being connected, at its rear end away from said leading edge, to a pressurized hot air circuit and, at its front end towards said leading edge, to an injector injecting a stream of said pressurized hot air into said annular chamber.
Thus, said stream of hot air flows through said annular chamber, heating it, before escaping to the outside through said communication orifice.
It has been found, in known cowls of this type, that the heating was not uniform in said annular chamber. This was because, near said injector, the walls of said annular chamber are raised to a very high temperature (several hundred degrees Celsius) whereas the regions of this chamber remote from said injector are subjected to relatively low temperatures. What this then means is that there is a risk that the walls of said annular chamber near the injector might be damaged, where as de-icing is not optimal in said regions remote from the injector.
It is an object of the present invention to overcome these drawbacks.
To this end, according to the invention, the air inlet cowl for a jet engine, particularly for an aircraft, provided with means for de-icing its leading edge and for this purpose comprising:
a hollow leading edge delimiting an internal annular peripheral chamber, closed by an internal partition and provided with at least one orifice placing said annular chamber in communication with the outside; and
a hot air supply pipe capable of being connected, at its rear end away from said leading edge, to a pressurized hot air circuit and, at its front end towards said leading edge, to an injector injecting a stream of said pressurized hot air into said annular chamber so that said stream of hot air flows through said annular chamber, heating it, before escaping to the outside through said communication orifice,
is noteworthy in that:
said communication orifice is calibrated to allow only some of said stream of hot air flowing through said annular chamber to escape to the outside, the rest of said stream being recirculated in this annular chamber; and inside said annular chamber, there is a mixer for forming, at each moment, a mixture of the stream of hot air being injected by said injector with the part of said previously injected stream of air that is recirculating.
Thus, the present invention makes it possible to even out the temperature of the stream of air flowing through the annular chamber with, as a consequence, elimination of the hot spots near the injector and better de-icing of those parts of the leading edge of the cowl which are remote from this injector.
In one particularly simple embodiment, said mixer may have a particular elongate shape, preferably the shape of a tube, the two ends of which are open, said mixer, at its upstream end arranged facing said injector, receiving both said stream of hot air being injected and said part of said stream of air that is recirculating, and delivering mixture at its downstream end, away from said injector.
It will be noted that, in the context of the present invention, said mixer may have any shape that makes it possible to obtain a uniform mixture of said two streams.
As a preference, in order to be easily housed in said annular chamber, said mixer is curved into a portion of an annulus, to correspond to the shape of said internal annular peripheral chamber.
To increase still further the uniformity in terms of temperature of the stream of hot air flowing through said annular chamber and therefore further improve the efficiency of the de-icing while at the same time more effectively eliminating hot spots, it is advantageous for said mixer to comprise means for causing said mixture of hot air stream to effect a swirling rotation in the manner of a cyclone. Thus, said stream of hot air passes through said annular chamber with a swirling motion.
Although said means for inducing swirl in said mixture of hot air may consist of vanes or blades arranged inside said mixer, it is advantageous for them to be able to use the energy of the hot air conveyed by said supply pipe.
To this end, said swirl-inducing means may comprise at least one auxiliary hot air injector arranged laterally and tangentially with respect to said mixer, downstream of the aforesaid injector. In this case, it is advantageous for said auxiliary injector to be supplied with hot air by a tapping off said supply pipe. The position of said auxiliary injector along the mixer, and the angle of inclination of the axis of said auxiliary injector to the axis of the mixer are parameters that can be used to adjust the swirl of the mixture of the streams of hot air. The number of auxiliary injectors used is also one such parameter.
In addition, the opening of the auxiliary injector or injectors in the region of the mixer preferably has a rectangular or elongate shape. This makes it possible to generate an auxiliary stream which has a higher pressure than the main stream, which improves the uniformity of the mixture and the swirl induced in the stream.
As an alternative, said means for causing the mixture of stream to swirl comprise at least one auxiliary hot air injector arranged in the region of the aforesaid injector. This or these auxiliary injector(s) may then be supplied with hot air directly by said supply pipe, as is the case of the aforesaid injector. It is then advantageous for the auxiliary injector(s) to form an integral part of the aforesaid injector.
Furthermore, said injector, which may be a part integral with or a part separate from the mixer, of any shape, is preferably arranged in the first half of the mixer.
It will be readily understood that, by virtue of the present invention, the thermal stresses experienced by the materials of which the leading edge is made are not as high whereas the de-icing efficiency is better. It is therefore possible to make said leading edge using more lightweight and less expensive materials and to reduce the temperature of the air tapped from the engine. As a consequence, the fuel consumption of said engine is reduced.